Two metre social distancing rule 'may not be far enough' to stop coronavirus
19 May 2020, 16:01
Government advice to stay two metres apart and socially distance may not be far enough to stop outdoor coronavirus transmission, a study has suggested.
Research from the American Institute of Physics has found saliva droplets can travel more than five metres in five seconds if exposed to a slight breeze of around 2.5mph.
Current government advice for England states that people should "should stay alert when they leave home" and "maintain social distancing."
It also confirms that people "should stay two metres apart from anyone outside of your household."
Professor Dimitris Drikakis, one of the authors of the study said shorter adults and children could be at greater risk if they are near the trajectory of the droplets.
He added: "The droplet cloud will affect both adults and children of different heights."
The study, which was published in the journal Physics of Fluids, looked at computer simulations of how coughing would cause saliva droplets to move through air, taking into account the way they disperse and the interactions of molecules of saliva and air.
Their simulation also considered the effects of humidity and temperature of the surrounding air.
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The team wrote: "Without surrounding wind speed, the droplets will fall to the ground in a short distance from the person exhaling or coughing. The present analysis shows that the range may not exceed one metre.
"At wind speeds from 4kph to 15kph, we found that saliva droplets can travel to distances up to six metres with decreasing concentrations and liquid droplets size in the wind direction.
"Our findings imply that depending on the environmental conditions, the two metres social distance may not suffice."
They add further studies are needed to determine the effect of ground surface temperature on the how saliva travels in air.
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Simon Clarke, associate professor in cellular microbiology at the University of Reading, who was not involved in the study, said: "The fact that droplets from a cough can travel for more than two metres is already understood, but this new study helps to provide more insight into the physical mechanisms at work as droplets travel through the air.
"This is a reminder that the two-metre rule is recommended, not because staying two metres away from all other people provides you with a force field against infection, but because it is a reasonable distance to stay away from people to reduce risk of infection."
He said that while staying two metres apart is better than keeping a one-metre distance, the protective effect of this measure is "not proportional to the distance".
Dr Clarke added: "The most important point to take away from this paper is not that we need to change guidelines on social distancing, but that coughing is one of the best ways to spread infected droplets if you're ill.
"So if you have a cough, stay at home until you're better - and if you cough unexpectedly when you are out and about, cough into your elbow. Then go home and stay there."
